>>Carth<<
Ehrm. Carth already had an adult son in Kotor 1, so he was father around the age of 12?

>>Revan<<
Also, Revan received the full Knight training, and went to search all Star Maps. He also conquered the Star Forge, joined a war. We know he was captured soon in the war too.
About the knight training, we know Obi-Wan was the perfect example. He was 25 years, but still had some lessons to learn. a.k.a: Go and do some more intensive missions. During the Clone Wars, they speeded up the Knight process, because of the lack of Jedi. Anakin was still around his early 20's though.
-At the end of his Jedi training, i think Revan was 26 years old.
-Finding the Star Maps: +2
-Conquering Star Forge, building army, wage war: +3
-Captured by Bastilla, rehabilitated: +1-2 years.

Total:
Revan might be 32-33 in Kotor 1.
Proof:
Bastilla uses a single saber in the Revan cutscene, wich shows she's still in her early training fase. Also, she's surrounded by other Jedi Knights, so she's still no good enough to do mission on her own. Also, in the Dantooine cutscene, we see Revan in his robes, so he must have left the order a little while ago. In a textbox below a loading screen, we read that Revan was captured relatively early in the war.

>>Bastilla<<
Maybe a bit older. She is ready to go alone on missions (with the PC), so eh's in her final padawan training stage, i think. 23-25 could be a bit more...realistic.

>>Candarous<<
Nothing to mention. We see his grey hair, hear his cracking voice, see him mumbling about his 'Basilisk War Droid.' He's definately in his 50's yes

Sorry to talk this much, but i always get the feeling people don't want Revan to be 30+. It's like they want to play with a person with a more similar ages like they do. I just think that, how older you are, how cooler you can become. Just watch Sin City, and watch Bruce Willis and Mickey Rourke.
For the SW fans, the coolest (LS) SW character is Yoda, and he's 900